Electrical heating device



Aug. 11, 1959 l. H. STEIN ELECTRICAL HEATING DEVICE Filed Nov. A 4, 1957 Fig. 3a

Fig. 5

INVENTOR.

I I$IDOREH.STEIN 26a? awg/ ATTORNEYS llnited States Patent-O ELECTRICAL HEATING DEVICE Isidore H. Stein, Clifton, NJ., assiguor to Allen B. Du Mont Laboratories, Inc., Clifton, NJ., a corporation of Delaware Application November 4, 1957, Serial No. 694,355

6 Claims. 01. 313-337 outer surface coated withelectron emissive material.

The heating element is generally inthe form of a longitudinal helical coil inserted lengthwise into the tube, causing the entire cathode to be heated. However, only a small portion of the total surface area at the end of the cathode is actually utilized for electron emission. A comparatively large amount of heat energy is used to produce a relatively small quantity of electron emission and much of the heat is dissipated and wasted. In view of the fact that present heaters are relatively large in size and require proportionately large filament power, miniaturization of the cathode, power supply, and other circuit components is made very diificult.

It is therefore the principal object of the present invention to provide a novel electrical heating device.

I in cross section; Fig. 4 represents a planar heater element in the form Fig. 2b is a side view showing the cross sectionof the circular coil form;

Fig. 3a illustrates a plan view of the ring shaped coil having a rectangular cross section;

Fig. 3b is a side view showing the rectangular coil form of a circular spiral grillwork; and

Fig. 5 shows a planar heater in the form of a circular sinuous or zigzag grillwork. In the embodiment shown in Fig. 1, the cathode is i in the form of a hollow cylindrical structure preferably having a greater diameter than height and including a closed circular end 12. The end 12 is coated with a layer of electron emissive material 14 on the exterior surface. The heating coil 16 is wound in a helical fashion, forming a ring or toroid. One face of the toroid is placed parallel and closely adjacent to or abutting the inner surface of end 12. The wire making up the coil is coated with a layer of insulating material, to prevent electrical contact. Heat confining or reflective metal disks 18, have age .to the cathode.

It is another object of this invention to furnish an electrode heating structure permitting more eflicient electron emission andrequiring less heating energy.

A further object is to provide a greater and more efficient concentration of heat close to an electron emissive surface and to permit maximum utilization of the thermal energy. v

; A still further object is to permit miniaturization of a cathode structure and utilization of smaller power supplies.

According to the present invention, a heater coil, preferably wound in the form of a thin circular disk or ring, is placed within a cylindrical cathode, transverse to the axis of the cathode and parallel and adjacent to the inner surface of the closed electron emissive end. The close proximity of the heating element to the emissive coated end furnishes a more direct concentration of heat permitting more eflicient electron emission and a reduction in energy and space requirements. A cathode is utilized which is considerably shorter than previous structures. Further conservation of thermal energy is achieved by inserting embossed reflective disks within the cathode structure behind the coil. Heat conduction between disks is kept at a minimum and non-useful heat radiation is reduced.

The detailed description and accompanying drawings, which follow, consider the instant invention in several particular configurations. It is to be understood that these embodiments are chosen for the purpose of explanation and illustration and are not to be construed as defining the limits of the invention.

Fig. l is a cutaway view of the cathode and heating assembly, showing a representative ring shaped heater coil;

Fig. 2a illustrates a plan view of the ring shaped coil having a circular cross section;

ing embossed or dimpled surfaces, are positioned one upon another, directly behind heater 16. The disks contact each other only at the high points of the surface projections, with the remaining areas being separated by space. The cathode assembly rests upon and isattached by fixtures 20 to supporting legs 22, and heater excitation is supplied by insulated leads 24 through the side walls of the cathode structure. Fixtures 20 and supports 22 are also used as electrical leads to provide volt- Line XX represents a reference plane for the coil which establishes its orientation with respect to the longitudinal axis of the cylindrical cathode. When heater coil 16 is energized, intense heat is applied to adjacent metallic surface 12 causing electron emission from the outer portion 14. Due to the position and structure of the coil, the heat is concentrated and applied almost directly to the area utilized. In addition, disks 18 prevent heat from being dissipated uselessly. The metal, lic surfaces of the disks reflect maximum heat back toward the closed end without absorbing significant amounts of energy, while the irregular or dimpled portions, provide minimum physical contact to reduce thermal conduction. In use, the entire cathode assembly is positioned within a cathode ray tube from which air has been removed, thus the space between disks is evacuated and aids in limiting heat transfer. Further insulation is provided by the small size of fixtures 20 which keep contact area and heat conduction between the cathode 10 and supporting structure 22 at a minimum. In this manner, heat energy is confined and excessive radia tion losses prevented.

Details of the ring or toroidal shaped heater winding 16 of Fig. 1 are shown in Figs. 2a and 2b which are respectively top and cross-sectional views. As shown in Fig. 1 this coil is placed immediately adjacent to or abutting the inner surface of the emissive coated end of the cathode.

Reference plane X-X, heretofore mentioned in connection with Fig. 1, is utilized for the purpose of claritying the description of the invention and to more readily relate the position of the heater with respect to various other component parts.

Another variation of the invention is a coil which has a rectangular section as shown in Figs. 3a and 3b. This rectangular configuration permits one flat surface of the coil to be placed in close contact with the cathode end, to apply heat more directly.

Another modification is shown in Fig. 4 which illustrates a planar spiral heater configuration having its entire structure located substantially in one plane, which is considered the reference plane. In this instancethe full face of the heater element is in close proximity or directly against the emissive, end of the cathode, and a moreefficieut concentration. ofheatris provided,-

Still another variation is that of Fig. which represents a= h ater. in. the form of a planar, sinuous or zigzag grillwork conformihg .to) the shape of a cylindrical cathode, The wires may be woundfabout: a notched supporting form such as a sheet of'mica and may be placed entirely above the form or wound alternately aboveand below. The heater is similarly positioned substantially inone plane, designated'as the reference plane, and supplies highly concentratedheat. p

. Further variations, such. as rectangular or elliptically shaped heaters may similarly be utilized .to conform to variousjcathode configurations. Other planar heaters may employ a wire'mesb" or screen type' structure. Sev-' eral1thicl'messes or layers ofwire'may also be used to provide moreheat; In addition, the cross-section of the ring shaped; coil maytake' various forms-such as oval or triangular.

It may thus be seen that the greater heat-concentration and reduction ofwasted energy provided by the instant invention resultin increased efficiency of electron emission usingaminimumofthermal energy. Spatial re: quirements are also reduced and miniaturization of the cathode assembly is made possible with a maximum proportion of the total cathode surface area being utilized for electron emission. Due to the increased eificiency, smaller filament power suppliescan furnish sufficient heat and emission. The-use of-"a.large number of turns of thin highly. resistant wire provides optimum. conditions for utilization of presently available low voltage supplies while'requiringonly small currents. The employment of small batteries and transistorization of circuitry is facilitated and in conjunction with. the instant inventionmay be applied advantageously to allow greater portability.

While only a few embodiments of the invention. have been illustrated, it' is apparent that: the device. is not limited to the exactiforms' or usesindicatedand that many variations may be madein the. particular design and con.- figuration without departing from: the. scope ofthe invention asset forth in theappended claims.

What is. claimed is:

l. Aneleotron emissiondevice for a cathode ray type tube comprising a; cylindricaljcathode having a closed end and, an electron; emissivecoating on the exterior surface of said end; a toroidal heater coil having a reference ode transverse to the axis of said cathode and parallel plane, saidplane positioned, within said cylindrical cathand closely adjacent to the interior surface of said end, whereby a high concentration of heat is supplied to said electron emissive surface; and a plurality of heat confining disks having flat reflective surfaces with embossments thereon, said disks. being positioned parallel and in close proximity to said heater, whereby heat loss is 2. A low powered cathode device of high thermal and electron emission" efficiency comprising a cylindrical catl'n ode have a closed end; a coating of electron emissive material placed on the exterior surface of said end; a toroid shaped heater coil having a reference plane, said plane positioned within said. cathode transverse to the axis of said cathod'e and parallel and in close proximity to the interior surface of said end; a plurality of heat confining metal disks placed closely adjacent and parallel to. saidiheater'alongitheportion of said heater away from said; cathode: end,: said. disks resting one. upon another and having flatv reflectivesurfaces with embossments thereon, said embossments providing sole contact be tween said: disk, surfaces and adjacent surfaces. whereby contact area and heat conduction are reduced and heat radiation-losses minimized.

3. The device of claim 2 wherein said toroid has a circular cross section.

. 4. The device of, claim 2' wherein said' toroid' has a rectangular cross: section.

5. The device of claim 2 wherein the diameter ofsaid cylindrical cathode is larger than the height.

6. The. deviceof claim 2'including a plurality Ofsup porting legs; aplurality of:fixtures attached to said legs and supporting; said cathode and disks, to provide an electrically conductive path between said cathode and legs and.v to further reduce surface contact area.

ReferencesCited in the file of this patent. UNIT ED STATES PATENTS 

